Solvent based paint removers have achieved considerable popularity and widespread use because of their ability to easily remove fully or partially cured coatings from substrates. Methylene chloride and other chlorinated hydrocarbon solvents have long been used in such formulations because of their effectiveness and low cost. However, methylene chloride is highly toxic and is suspected of being a potential carcinogen. In addition, methylene chloride and other halogenated compounds are environmentally undesirable due to their suspected role in the destruction of the ozone layer. Since paint removers are commonly rinsed off substrates after use using water, contamination of ground water by such solvents is also a potential problem.
N-Methyl pyrrolidone (NMP) is a preferred substitute for chlorinated solvents in coating remover formulations because of its effectiveness, low toxicity, biodegradability, and high flash point. Although typically not as fast as methylene chloride in "lifting" the paint from a substrate, NMP has a much lower vapor pressure and thus can be readily used at elevated temperatures or in a soak tank. In addition, NMP has such a low rate of evaporation that lifted coatings may be readily peeled from the substrate many hours after lifting. In a methylene chloride-based formulation, the lifted film will generally re-adhere to the substrate if the coating is not mechanically removed soon after lifting occurs. Several applications of a methylene chloride-based formulation may be necessary to completely remove thick or multiple layer coatings due to the rapid rate of solvent evaporation, while a single application of an NMP-based formulation may be sufficient.
A deterrent to the use of N-methyl-2-pyrrolidone as the primary solvent in coatings remover formulations has been the relatively high cost of NMP. For this reason, a number of solvent blends containing NMP have been developed having performance approximately equivalent to that of pure NMP For example, a low toxicity paint remover containing NMP and an aromatic hydrocarbon is described in U.S. Pat. No. 4,120,810. U.S. Pat. No. 4,749,510 teaches a solvent blend effective as a coatings remover in which NMP, an aromatic hydrocarbon, and formic acid are combined with surfactants, thickeners, and corrosion inhibitors. NMP has also been blended with benzyl alcohol and aromatic naphtha to obtain a useful paint remover, as taught in U.S. Pat. No. 4,732,695. U.S. Statutory Invention Registration H300 describes NMP and monoethanol amine mixtures which are particularly effective on thick epoxy coatings. A paint stripper composition containing predominatly oxo-hexyl acetate and cyclohexanone together with minor amounts of N-methyl-2-pyrrolidone is disclosed in U.S. Pat. No. 4,666,626. A blend of NMP, alkanolamine, and an alkali or alkaline earth metal base has been found to be effective in removing paint from a substrate as shown in U.S. Pat. No. 4,276,186. U.S. Pat. No. 4,085,059 teaches a foam-type coating remover containing NMP and a water based carrier.
N-Methyl-2-pyrrolidone is clearly a preferred solvent component in paint stripping applications due to its effectiveness, low volatility, low toxicity, and biodegradability. However, there is a need for an improved coatings remover composition wherein NMP is diluted with less expensive solvents to reduce the cost of the formulation while retaining the desirable performance characteristics of the N-methyl-2-pyrrolidone.